1. Field of the Invention
The present invention relates to a communications terminal unit to be connected to an Internet protocol (IP) network and a public switched telephone network, and to a method for controlling the unit. More specifically, the invention relates to a communications terminal unit having the function of automatically determining whether to originate a call over an IP network or over a public switched telephone network in accordance with call destination specification information input at the time of origination of a call, as well as to a method for controlling the unit.
2. Description of the Related Art
For example, some facsimile machines are connected to both an IP network and a public switched telephone network. In the case of a related-art facsimile machine of this type, a user selects “FAX,” in which a call is originated over the public switched telephone network, or “iFAX,” in which a call is originated over the IP network.
However, in the case of the facsimile machine which originates a call in accordance with the user's selection of a network, an indispensable feature for all users is the ability to ascertain whether or not a call can be originated to a call receiver over the IP network or whether or not origination of a call over the public switched telephone network incurs a low communication cost.
However, in reality, it is extremely difficulty for all users to ascertain whether or not a call can be originated to a call receiver over the IP network or whether or not origination of a call over the public switched telephone network incurs a low communication cost.
For this reason, there may arise, for example, a case where a waste of communication cost occurs when a call is originated over the public switched telephone network in spite of the possibility of originating a call over the IP network.
In contrast, when, in spite of the impossibility of originating a call over the IP network, an attempt is made to originate a call over the IP network, a communication error arises. In this case, origination of a call over the same network is repeated only a predetermined number of times at predetermined re-dialing intervals. In contrast to a case where the party on the other end of the line is busy, communication cannot be established permanently, because a call is originated over a network over which a call essentially cannot be originated.
As mentioned above, in the case of the related-art facsimile machine connected to both the IP network and the public switched telephone network, the user selects one from the IP network and the public switched telephone network, thereby originating a call. However, it is difficult for all users to ascertain whether or not a call can be originated to a call receiver over the IP network or whether or not origination of a call over the public switched telephone network incurs a lower communication cost.
Therefore, for example, an inevitable occurrence is selection of an inappropriate network at the time of origination of a call; namely, an unavoidable outcome is that a call is originated over the public switched telephone network in spite of the possibility of originating a call over the IP network, or an attempt is made to originate a call over the IP network despite the impossibility of doing so. The former case incurs a waste of communication cost, and the latter case induces a communication error, thus resulting in an incommunicable state.